<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
<HTML>
<HEAD>
<TITLE>80386 Programmer's Reference Manual -- Section 9.5</TITLE>
</HEAD>
<BODY STYLE="width:80ch">
<B>up:</B> <A HREF="c09.htm">
Chapter 9 -- Exceptions and Interrupts</A><BR>
<B>prev:</B> <A HREF="s09_04.htm">9.4  Interrupt Descriptor Table</A><BR>
<B>next:</B> <A HREF="s09_06.htm">9.6  Interrupt Tasks and Interrupt Procedures</A>
<P>
<HR>
<P>
<H1>9.5  IDT Descriptors</H1>
The IDT may contain any of three kinds of descriptor:
<UL>
<LI> Task gates
<LI> Interrupt gates
<LI> Trap gates
</UL>

<A HREF="s09_05.htm#fig9-3">Figure 9-3</A>
  illustrates the format of task gates and 80386 interrupt gates
and trap gates. (The task gate in an IDT is the same as the task gate
already discussed in 
<A HREF="c07.htm">Chapter 7</A>.)
<P>
<A NAME="fig9-3">
<PRE>Figure 9-3.  80306 IDT Gate Descriptors</PRE>
<P>
<PRE>
                                80386 TASK GATE
   31                23                15                7                0
  +-----------------+-----------------+---+---+---------+-----------------+
  |#############(NOT USED)############| P |DPL|0 0 1 0 1|###(NOT USED)####|4
  |-----------------------------------+---+---+---------+-----------------|
  |             SELECTOR              |#############(NOT USED)############|0
  +-----------------+-----------------+-----------------+-----------------+

                                80386 INTERRUPT GATE
   31                23                15                7                0
  +-----------------+-----------------+---+---+---------+-----+-----------+
  |           OFFSET 31..16           | P |DPL|0 1 1 1 0|0 0 0|(NOT USED) |4
  |-----------------------------------+---+---+---------+-----+-----------|
  |             SELECTOR              |           OFFSET 15..0            |0
  +-----------------+-----------------+-----------------+-----------------+

                                80386 TRAP GATE
   31                23                15                7                0
  +-----------------+-----------------+---+---+---------+-----+-----------+
  |          OFFSET 31..16            | P |DPL|0 1 1 1 1|0 0 0|(NOT USED) |4
  |-----------------------------------+---+---+---------+-----+-----------|
  |             SELECTOR              |           OFFSET 15..0            |0
  +-----------------+-----------------+-----------------+-----------------+
</PRE>
<P>
<HR>
<P>
<B>up:</B> <A HREF="c09.htm">
Chapter 9 -- Exceptions and Interrupts</A><BR>
<B>prev:</B> <A HREF="s09_04.htm">9.4  Interrupt Descriptor Table</A><BR>
<B>next:</B> <A HREF="s09_06.htm">9.6  Interrupt Tasks and Interrupt Procedures</A>
</BODY>
